How Hot Is the Moon?
The sun beats down on the face of the moon without mercy and the heat generated is almost twice that of the hottest day on earth. This scorching goes on without letup for fifteen earth days and nights, for the length of each lunar day is a little longer than two earth weeks the night which follows is equally long and bitterly cold.
During the lunar day, in most regions, the surface rocks are hot enough to boil water into steam. During the chilly night the temperature drops to about minus 240 degrees Fahrenheit.
The moon, like the earth, revolves on its axis and also, like the earth, its axis is tilted at an angle to its orbit. This gives the moon polar regions. In a modest way the moon has yearly seasons. There are times when the North Polar Region enjoys the midnight sun. At this time the South Polar Region is suffering a long polar night. As on earth, the polar climates alternate with the seasons.
The moon, of course, circles the earth as the earth circles the sun. At times it is nearer and at times further away from the sun than is the earth, but the difference is never very great.
Why, then, does the moon have such extremes of heat and cold? The answer is that the earth has an atmosphere and the moon does not. Of the total sunlight which strikes the earth’s atmosphere more than half is reflected back into space. Much of the heat which reaches the earth is held there, also by the atmosphere,
Thus the earth receives less of the sun’s heat and much of what it does receive it can hold on to after the sun has gone to bed. The moon has no useful blanket of air to modify the blazing heat of the sun. It has no atmosphere to hold in the day’s heat after the sun sets.
It so happens that the moons day and night period is equal to the time it takes to orbit the earth, its revolution equals its rotation and so the same side of the moon is always facing towards the earth.
It takes one lunar month for a day and night to pass over this face of the moon. We see only the part which is lit with the glory of the sun. The rest is in the darkness of night. This explains the changing phases of the moon.